CDK6 and esophageal squamous cell carcinoma: Among all 38 superficial ESCC samples, recurrent focal amplifications of 11q13.3 (FGF4 and FGF19), 8q24.21 (MYC), 7q22.1 (CDK6) and deletions of 9p21.3 (CDKN2A), 3p12.3 (MITF), 2q22.1 (LRP1B), 13q14.2 (RB1) which were previously reported in all stage of ESCC [8, 11, 12, 26–30] were also found in our study.